Vibration isolation insert for aircraft floor planels and the like

ABSTRACT

An insert used to connect aircraft floor panels, and the like, to supporting structure includes features which function to isolate the supported panel from vibrations in the supporting structure. The isolation of the panels leads to reductions in SIL (Speech Interference Level) noise within aircraft cabins. The insert consists of internal and external rigid components separated by a contoured elastomeric component. The elastomeric component is preloaded when installed via a fastener extending through the inner rigid component and attaching to the supporting structure. The outer and inner rigid components are sized such that the inner rigid component will not pass through the outer rigid component, thus providing a safetied installation of the panel. The elastomeric component extends below the bottom of the outer rigid component and provides soft snubbing against the supporting structure during loading of the panels. This allows some level of isolation while restricting motion of the panels.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to an insert for an aircraft floor panel,or the like, used to attach the panel to a supporting structure. Moreparticularly, the present insert has the capability to isolate the panelfrom the vibrational energy propagated through its support.

It has been determined that a large contribution to speech interferencelevel (SIL) noise, in certain commercial aircraft, is radiated by thefloor panels. Apparently, the vibration that is transmitted along thebeams which support the panels effectively vibrate the panel similar tothe way a speaker diaphragm is vibrated. In order to reduce weight,these panels are typically made of an aluminum honeycomb, or otherhighly rigid constructions, that are highly susceptible to vibration.One current method of attaching these panels to the support beamsemploys metal inserts that are staked to the floor panel and secured tothe upper surface of the support beam using a screw inserted through theinsert and threaded into a clip nut. This technique amounts to hardmounting the panel to the support providing a solid path fortransmission of vibration.

The present invention significantly reduces SIL noise within thepassenger compartment. The attachment insert of the present inventioncomprises a) a substantially cylindrical rigid outer member secured inan aperture in the floor panel and having an axial throughbore defininga minimum internal dimension of said outer member; b) a contouredelastomeric member bonded to said axial throughbore, said elastomericmember having a central axial opening therethrough and a portionsurrounding the central axial opening that extends below a lowermostportion of said outer member; and c) a rigid inner member having asubstantially cylindrical first portion of a first diameter which ispress fit into said central axial opening of said elastomeric bushingand a shorter cylindrical second portion which has a second largerdiameter than said first portion, said second portion generallyoverlying said contoured elastomeric member, rigid inner member havingan axial fastener-receiving throughbore permitting attachment to saidsupport. The outer diameter of the second portion is greater than theminimum internal dimension of the first member. As a result, the insertof the present invention is safetied against possible loss of elastomerintegrity. The outer member has a flange which is used to bond theinsert to the lower surface of the panel and provides pull-throughresistance.

The contoured elastomer has a sleeve portion that extends along theouter periphery of the shank of the inner member and has a longer axialextent than said shank. In addition, the elastomeric member has a solidannulus that extends below the surface of the flange of the outermember. The excessive length of the sleeve results in the elastomerbeing preloaded in its secured position. The annulus provides a snubbingring for the panel when the panel is loaded as by a passenger walking, abeverage/food cart, or by carry-on luggage placed beneath the seat. Theannulus prevents the loading of the panel from creating a solid path;accordingly, the panel remains isolated from the vibrating supportsurface such that the SIL noise in the passenger compartment is stillreduced.

Various other features, advantages and characteristics of the presentinvention will become apparent after a reading of the followingspecification.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention are described inaccordance with the attached drawings in which

FIG. 1 is a cross-sectional front view of a first embodiment of theinsert of the present invention as seen along line 1--1 in FIG. 3;

FIG. 2 is a top view of the first embodiment of the insert,approximately, actual size;

FIG. 3 is a bottom view of the first embodiment of the insert;

FIG. 4 is a cross-sectional front view of a second embodiment of theinsert shown installed in a panel; and

FIG. 5 is an isometric view of the aircraft fuselage depicting theplacement of a floor panel across a plurality of beams.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first preferred embodiment of the present invention is shown in FIG. 1generally at 20. Rigid outer member 22 is shown as having asubstantially cylindrical body portion 24 and a flange 26 which extendsfrom a lower edge. Other shapes could, of course, be used; however,cylindrical will generally be preferred for ease of placement in thefloor panels 11 (FIG. 4). Drilling a round hole will be simpler thanpunching out some other shape. The upper rim 28 of cylindrical bodyportion 24 has a reduced wall thickness that will be rolled over in astaking operation to secure it to panel 11. In addition, an adhesivewill be applied to the upper surface 27 of flange 26 (FIG. 2) to secureit to the lower surface of panel 11.

Rigid outer member may be metallic, made of metals including aluminum,powdered titanium, or similar light weight metals, in which case thestaking operation is mechanical. As an alternative, rigid outer member22 may be made of an engineered plastic, such as ULTEM available fromGE, for example. With such a plastic, an ultrasonic staking procedurecan be used to form the upper flange to capture plate 11. Certaincomposites may also be appropriate for making the rigid members of thisinvention, such as glass or carbon fiber reinforced plastics. Rigidouter member 22 has a minimum internal dimension formed by inwardlyprojecting annulus 30.

A contoured elastomeric member 32 is bonded to an internal portion ofrigid outer member 22. This bond may be either chemical in nature, i.e.,produced using an adhesive, or mechanical, i.e., the elastomer may bemolded in place. The elastomer is preferably one which will providemedium damping and has reasonable low temperature flexibility. Asuitable elastomer is available from Lord Corporation and is identifiedas SPE®I. A portion of the elastomeric member 32 is contained withinrigid outer member 22 and a portion extends beneath member 22. Theelastomeric member 32 has a first predetermined axial length extendingalong the axis of the rigid outer member 22 and a central axial opening33 that extends therethrough. The portion extending below member 22 isan annulus 34 made up of a plurality (preferably three) of load bearingportions 36 with a like plurality of intermediate bridging portions 38.An annular ring 40 underlies a portion of rigid outer member 22. Theportion of the elastomeric member 32 contained within the rigid outermember has a configuration identical to that of annulus 34 with theexception of the absence of a ring corresponding to ring 40.

A third element of insert 20 is rigid inner member 42. Inner member 42is preferably made of the same material as that used for rigid outermember, although a different material could be used. Rigid inner member42 has a first generally cylindrical portion 44 having a first outerdiameter that is press fit into central axial opening 33. Inner member42 has a second shorter generally cylindrical portion 46 which has adiameter which overlies the elastomeric member 32. The maximum diameterof second cylindrical portion 46 exceeds the minimum internal dimensionof annulus 30. In this manner, insert is safetied against the possibleloss of integrity of the elastomeric member 32, i.e., the floor panel 11cannot lift up off of the support 13 to which it is attached. Innerrigid member 42 has an axial fastener-receiving throughbore 48. Theoperation of insert 20 will be described in conjunction with the secondembodiment.

FIG. 4 depicts a second embodiment generally at 20'. In this embodiment,the upper rim used to roll over on the panel 11 is omitted. The adhesiveapplied to upper surface 27' of flange 26' is sufficient to secure thepanel in place making the staking operation unnecessary, resulting insignificant savings in installation cost and time. All other features ofthis embodiment are identical to the first embodiment. As shown in FIG.4, floor panel 11 is secured to the upper flange 13 of an I-beam supportby a threaded fastener 15 and a clip nut 17. Nut 17 is slipped overflange 13, a hole 19 having been drilled in therein. Screw 15 is theninserted through fastener-receiving throughbore 48', and the insert 20'and panel 11 which is adhered thereto, are fastened to support flange 13by threading screw 15 into clip nut 17. The predetermined axial lengthof the elastomeric member 32 exceeds the length of rigid inner member 42(FIG. 1). Accordingly, as the fastener 15 is tightened, the elastomer ofmember 42 will be preloaded assuring continuous contact and consistentperformance.

Elastomeric member 32' isolates outer member 22' from inner member 42'and, hence, floor panel 11 from support flange 13. Accordingly, certainvibrations being transmitted through flange 13 will not be transmittedinto the floor panel 11 or the associated passenger compartment. Thepanel 11 will normally occupy an elevated position relative to flange 13as depicted in FIG. 4. Should the panel be subjected to loading due to,for example, someone walking on it, beverage cart passing across it orcarry-on luggage being stored on panel 11, the elastomer aroundload-carrying protrusions 36 will permit the panel to deflect downwarduntil ring 40' engages flange 13. Ring 40' gently snubs this movementand even when under load, the panel 11 remains isolated from flange 13.

Flight tests of the present insert 20 demonstrated SIL noise reductionsin the passenger compartment including approximately 5 decibels in the500 Hz range and 10 dB at each of the 2000 Hz and 4000 Hz levels.Approximately forty inserts 20 are used to secure a 2'×4' floor panel 11in position as depicted in FIG. 5. The inserts 20 used in the testemployed outer and inner rigid members 22 and 42 that were made ofaluminum.

Various changes, alternatives and modifications will become apparent toa person of ordinary skill in the art after a reading of the foregoingspecification. It is intended that all such changes, alternatives andmodifications as come within the scope of the appended claims beconsidered part of the present invention.

What is claimed is:
 1. An insert securing an aircraft floor panel to a support structure wherein vibrations transmitted by said support structure are isolated from said floor panel, said insert comprisinga) a substantially cylindrical rigid outer member secured in an aperture in said aircraft floor panel and having an axial throughbore defining a minimum internal dimension of said outer member; b) a contoured elastomeric member bonded to said axial throughbore, said elastomeric member having a central axial opening therethrough and an elastomer portion surrounding said central axial opening that extends below a lowermost portion of said outer member, said elastomer portion being positioned proximate to but in nonengaging relationship with said support structure and being deflectable into snubbing engagement with said support structure upon application of sufficient vertical load; and c) a rigid one-piece inner member having a substantially cylindrical first portion of a first diameter which is press fit into said central axial opening of said elastomeric bushing and an integral shorter second portion which has a second larger diameter than said first portion, wherein said second larger diameter of said integral shorter second portion exceeds said minimum internal dimension of said outer member to safety the insert against potential loss of elastomer integrity, said integral second portion generally overlying said contoured elastomeric member, said rigid inner member having an axial fastener-receiving throughbore permitting attachment to said support structure.
 2. The insert of claim 1 wherein said cylindrical rigid outer member has a radially directed lower flange which underlies a peripheral portion of said aperture in said floor panel.
 3. The insert of claim 2 wherein said lower flange is non-circular.
 4. The insert of claim 2 wherein said contoured elastomeric member has an annular portion which underlies at least a portion of said lower flange.
 5. The insert of claim 2 wherein said insert is attached to said floor panel by means including adhesive between said lower flange and said floor panel.
 6. The insert of claim 5 wherein said attaching means further includes an overlying flange which is configured to overlie a peripheral portion of said aperture in said floor panel.
 7. The insert of claim 1 wherein said contoured elastomeric member has a portion which extends below said first portion of said rigid inner member and is configured to receive a preload when said insert secures said aircraft floor panel to said support structure.
 8. The insert of claim 7 wherein said portion which extends below said rigid one-piece inner member comprises an annulus made up of a plurality of load bearing portions interconnected by a like plurality of bridging portions.
 9. The insert of claim 1 wherein the outer and rigid one-piece inner members are made of a material in a group consisting of metals, engineered plastics, composites and combinations thereof. 